Boxed question marks instead of text

Thank you for that comprehensive follow up. I'm heartened to learn that it has been resolved.

"Safe Mode" is the easiest way to reset the Mac's font cache files. After finding Apple's instructions for booting Safe Mode on Silicon Macs somewhat lacking in detail, I decided to expand upon them:

1. Start with a Mac powered on in the usual manner, logged into your User Account.
2. Shut down the Mac using  > Shut Down...
3. Wait until the Mac actually shuts down. You can confirm it has actually shut down by pressing the Caps Lock key. The Mac will begin to start, but the Caps Lock LED will not illuminate until after the Apple logo appears. If that did not happen then it was not shut down, so you might as well start over at Step 1.
4. Press and hold the power button / Touch ID button. "Continue holding for startup options..." will appear, followed a second or two later by "Loading startup options...". If that does not happen, you might as well start over from the beginning.
5. When the "hard disk" and "gear" icons appear, release the power button.
6. Select (momentarily click) the startup disk. "Continue" will appear beneath it.
7. Press either Shift key. The "Continue" button legend should change to "Continue in Safe Mode".
8. Continue holding the Shift key and click that button. You can release it when the indeterminate progress indicator "spinner" appears.
9. The usual Login screen will appear, but "Safe Boot" should appear in red at the upper right of the Mac's menu bar.
10. Log in in the usual manner. Once logged in, it might not be obvious the Mac is in Safe Mode. You can confirm that it is with  > System Information > Software. Under System Software Overview, the words Boot Mode: Safe should appear. Get system information for your Mac - Apple Support describes how to open the System Information app.

Ten steps instead of four, but it describes what you need to do in greater detail.

System Software:

    macOS Monterey 12.2 (21D49)

That's out of date by more than a year: Update macOS on Mac - Apple Support

It may or may not fix what's wrong, but there is no disadvantage to keeping macOS updated.

    [Loaded] Suitcase Fusion (Not signed - installed 2022-01-25)

        Application

        /Applications/Extensis Suitcase Fusion/Suitcase Fusion.app

"Suitcase Fusion" is a font management utility, and is likely to be related. It may require an update also.

https://www.extensis.com/support/suitcase-fusion-support-guide/

You already performed some good troubleshooting, to include Restore fonts that came with your Mac using Font Book - Apple Support.

The fact it does not occur in "Safe Mode" suggests a software conflict of some sort. In an effort to identify what it might be, consider running EtreCheck and posting its report in a reply to this Discussion. How to use the Add Text Feature When Posting Large Amounts of Text, i.e. an Etrecheck Report - Apple Community includes instructions and a download link.

I don't really know what to do here, but this has also been happening to my iMac for some time and it's becoming quite a chore to navigate online and work when these boxes/question marks pop up or make an entire page unreadable, or if it pops up in my email. I have to go into inspector mode to highlight a line of text and deselect the font in the panel to see if that will trigger it to fix itself, but I can't keep doing this for every page with these issues all the time. I have no font duplicates, and preferences in Firefox to enable pages to use their own is on. I've cleared cache etc...and done many similar fixes suggested, except safe mode. I'm not quite understanding in typical lay terms how to do that if someone could please simplify? I am on an iMac running Monterey and use Firefox browser. That said, this is a potential workaround, but why is this happening. This never happened before. I see many online having these issues, with very little solutions being given. I appreciate any help.

Incidentally just an hour ago, December 9, 2023, I had composed a blessing in the iPhone App NOTES, sent it to my friend via FB Messenger and I had noticed there were TWO unexplained question marks in an off centered square within different parts of the message. Confused, I came upon this thread and am stuck in a quandary with no answers as to why. Especially so when reading here that it was a Mac issue. Odd, right?